Geophysical data from the Antarctic Peninsula continental shelf reveal streamlined subglacial bedforms in a cross-shelf trough. Bedforms exhibit progressive elongation with distance along the trough, and record flow of a paleo-ice stream from the Antarctic Peninsula Ice Sheet during the last glacial maximum. Downflow evolution of the bedforms indicates increasing flow velocities as the ice stream traversed the shelf. This, in turn, is related to a transition from crystalline bedrock on the inner shelf to a soft sedimentary substrate on the outer shelf. Although streaming flow operated across both substrates, the highest flow velocities occurred over the soft bed. Spatial variation in the inferred nature of fast-flow, from sliding to subglacial sediment deformation and/or ploughing, was also lithologically controlled. These data highlight the control of subglacial geology on ice-stream dynamics in the geological record and demonstrate a direct relationship between the formation of streamlined subglacial bedforms and paleo-ice streams.